Element and isotope mass balance in mixing
For closed mixing by mass of two endmembers, concentration is C_mix=fC₁+(1−f)C₂.
Key knowledge
For closed mixing by mass of two endmembers, concentration is C_mix=fC₁+(1−f)C₂. An isotope ratio R=N/D mixes according to denominator-isotope amounts: R_mix=[fd₁R₁+(1−f)d₂R₂]/[fd₁+(1−f)d₂]. Here d is the denominator-isotope amount per unit material mass. A straight arithmetic mixture of ratios is valid only with the corresponding denominator weighting.
Values and equations
C_mix=fC₁+(1−f)C₂; R_mix=[fd₁R₁+(1−f)d₂R₂]/[fd₁+(1−f)d₂]
- f
- mass fraction contributed by endmember1 1
- C₁,C₂,C_mix
- element concentration on one consistent mass basis kg kg⁻¹
- R₁,R₂,R_mix
- numerator/denominator isotope ratios 1
- d₁,d₂
- denominator-isotope amount per material mass mol kg⁻¹
Conditions and scope
- 0≤f≤1, additive material masses, unchanged isotope inventory, common isotope-ratio convention and positive total denominator amount.
- Do not silently use total-element concentrations as exact denominator-isotope amounts when isotopic fractions differ. Fractionation, reaction, decay or external gain/loss during mixing need additional terms; a linear ratio plot can have a mixing origin.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read normalized parent/daughter ratios and explicit component-conservation bodies. Both mixing formulas are disclosed direct atom/component bookkeeping derivations, not claimed as printed Nelson equations. This exact denominator weighting avoids an unsupported simple isotope-ratio average.
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Entry details
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- uni-earth-element-isotope-mixing
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- core.1
- Structured reference record
- University core expansion